Rats, mice, and relatives are found throughout the world except for the extreme polar regions of Earth.

Rats, mice, and relatives live in many different habitats including open flatlands, savannas (flat grasslands), grasslands, prairies, steppes (treeless plains that are often somewhat dry and grass-covered), woodlands, forests, deserts, scrublands, foothills, jungles, rainforests, wetlands, cultivated lands and fields, and along waterways and water bodies. They are found from dry temperate (mild) climates to wet tropical environments.

Most species of rats, mice, and relatives eat at least a few of the following foods: grasses, seeds, grains, root vegetables such as bulbs and tubers, green plant parts, conifer needles, nuts, berries, fruits, insects and insect larvae (LAR-vee), fish, lizards, frogs, baby birds, crabs, tadpoles, salamanders, fungus, lichens, mosses, other small vertebrates (animals with a backbone) and invertebrates (animals without a backbone), and carrion (decaying animals).

Rats, mice, and relatives are generally considered pests in agricultural and forested lands. Large species are often trapped for their fur. Some species carry diseases that can sicken and kill people. Rats, mice, and relatives are frequently used as laboratory research animals. Some, such as hamsters and gerbils, are kept as pets. They are often important in maintaining a healthy ecosystem in their natural habitats.

Almost 450 species of murids are listed on the World Conservation Union's (IUCN) Red List. Of these, twenty-one are Extinct, died out; fifty are Critically Endangered, facing an extremely high risk of extinction in the wild; seventy-four are Endangered, facing a very high risk of extinction in the wild; and 110 are Vulnerable, facing a high risk of extinction in the wild.

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Rats, mice, and relatives, sometimes called murids (MYOO-rids; members of the family Muridae), are divided into seventeen subfamilies, including voles and lemmings, hamsters, Old World rats and mice, South American rats and mice, and many others. As a result of the large number of species, there is much variation in the physical characteristics of murids. Voles and lemmings are small rodents with …

Rats, mice, and relatives are active during the day, at night, or both night and day (depending on the species). For their size, they can be very aggressive to predators and even to other members of their species. The rodents can be vocal, with various communicative sounds such as chattering, screaming, and whistling. They set up territories and defend them vigorously. Murids are sometimes found a…

Physical characteristics: The muskrat has dark brown upperparts and light grayish brown underparts. Adult head and body length is 15.5 to 24.5 inches (40 to 62 centimeters) and weight is 1.1 to 4 pounds (0.55 to 1.82 kilograms). Geographic range: They range in the western part of North America, and have also been introduced into Europe, Asia, and South America. Habitat: Muskrats are found around w…

Physical characteristics: Norway lemmings have brown to black fur. Adult head and body length is 3 to 7 inches (8 to 17.5 centimeters) and weight is 0.5 to 4.5 ounces (20 to 130 grams). Geographic range: They are found in Scandinavia (the northern European region of Norway, Sweden, Denmark, Finland, Iceland, and the Faroe Islands). Habitat: These lemmings inhabit open tundra and subarctic bog area…

Physical characteristics: Black-bellied hamsters have a short hairless tail; a thick fur that is reddish brown above with white patches on the flanks, nose, cheeks, and throat; and black underparts. Males are larger than females. Adults are 8 to 12 inches (20 to 34 centimeters) long and weigh between 4.5 and 36.3 ounces (112 to 908 grams). Geographic range: These hamsters are found in central and …

Physical characteristics: Australian jumping mice have light sandy brown to gray upperparts; white to light gray bellies; long tails with fine fur; large ears; narrow, large hind feet; and sebaceous (secretion) glands that are used for territorial marking. Adults have a body length of 3.9 to 5.9 inches (10 to 15 centimeters); tail length of 3.5 to 8.2 inches (9 to 21 centimeters); and weight of 0.…

Physical characteristics: Hispid cotton rats have a gray streaked coat with blackish or dark brownish hairs; pale to dark grayish underparts; dark tail; and five pairs of nipples, although some have four or six pairs. Adults have a total length of 8.8 to 14.4 inches (22.4 to 36.5 centimeters); tail length of 3.2 to 6.5 inches (8.1 to 16.6 centimeters); and weight of 3.5 to 8 ounces (100 to 225 gra…

Physical characteristics: Gambian rats are fairly large rodents with short fur that can range from soft to coarse. Some species are mottled, or splotched, with darker colors or may have an indistinct white line running across the shoulders. They have large ears; dark rings around the rather small eyes; a long and narrow head and face; cheek pouches to collect food and other materials; smooth incis…

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